The present invention relates generally to agitation devices and dispensing systems incorporating such agitation devices, and, more particularly, to agitation devices and dispensing systems (for example, injection systems) for use in connection with delivery of a multi-component medium to a patient.
In a number of medical procedures, it is desirable to inject a multi-component injection medium into a patient. An example of such a medical procedure is ultrasound imaging.
Ultrasound imaging creates images of the inside of the human body by broadcasting ultrasonic energy into the body and analyzing the reflected ultrasound energy. Differences in reflected energy (for example, amplitude or frequency) appear as differences in gray scale or color on the output images. As with other medical imaging procedures, contrast-enhancing fluids (often referred to as contrast media) can be injected into the body to increase the difference in the reflected energy and thereby increase the gray scale or color contrast displayed in the image (that is, the image contrast) viewed by the operator.
For ultrasonic imaging, the most common contrast media contain many small bubbles. The difference in density of bubbles when compared to water, and thus their difference in sound transmission, makes small gas bubbles excellent means for scattering ultrasound energy. Small solid particles can also serve to scatter ultrasonic energy. Such particles are typically on the order of 1 to 10 microns (that is, 10−6 to 10−5 meters) in diameter. These small particles can pass safely through the vascular bed.
Contrast media suitable for use in ultrasound are supplied in a number of forms. Some of these contrast media are powders to which liquid is added just before use. The powder particles cause a gas bubble to coalesce around them. The powder must be mixed with a liquid, and the mixture must be agitated with just the right amount of vigor to obtain the optimum creation of bubbles. Another type of contrast medium is a liquid that is agitated vigorously with air. There are no solid particles to act as nuclei, but the liquid is a mixture of several liquid components that make relatively stable small bubbles. A third type of contrast medium uses “hard” spheres filled with a gas. These contrast media are typically supplied as a powder that is mixed with a liquid. The goal is to suspend the spheres in the liquid without breaking them. Even though such spheres have a shell that is hard compared to a liquid, they are very small and relatively fragile. It is also possible for the solid particles themselves to act to scatter ultrasonic energy, but the acoustical properties of the solid spheres are not as different from water as those of a gas so the difference in reflected energy is not as dramatic.
Contrast medium particles also enhance other modes of ultrasonic imaging. For example, when the particles are carried along in the blood stream, the reflected energy is Doppler shifted. This Doppler shift allows an estimation of the speed of blood flow. Bubbles can also be excited so that they radiate ultrasonic energy at the second harmonic of the incident ultrasonic energy. This harmonic imaging is dependent upon the non-linearity of the reflectors. Gas bubbles work well as harmonic reflectors.
After mixing/preparation as described above, the contrast medium is drawn into a syringe or other container for injection into the patient. Typically, the fluid is injected into the vein in the arm of the patient. The blood dilutes and carries the contrast medium throughout the body, including to the area (i.e., the region-of-interest or ROI) of the body being imaged.
It is becoming more common for a microprocessor controlled power injector to be used for injecting the contrast medium. Compared to a hand injection of contrast, this has the benefit of maintaining a consistent flow over a long time, thereby providing a consistent amount of contrast medium (number of particles) in the blood stream. If there are too few particles, for example, there is insufficient image contrast and the diagnosis cannot adequately be made. If too many particles are present, too much energy is reflected, resulting in blooming or saturation of the ultrasound receiver.
Although a power injector can inject contrast medium at a constant flow rate, there must be a constant number of bubbles per volume of fluid injected to provide a constant image contrast. Because a gas is significantly less dense than water and other liquids, however, gas bubbles will rise in a liquid. The rate of rise is related to the diameter of the gas bubble. This density difference provides a useful tool to quickly separate large bubbles created during the initial mixing. However, the small bubbles desired for image enhancement will also rise slowly. Solid particles, on the other hand, will tend to settle or sink because most solids are more dense than water. Many minutes can elapse between the initial mixing of the contrast medium and the injection into the patient, and/or the injection itself may be several minutes in duration. If the concentration of particles changes, the image contrast may be degraded.
It is, therefore, very desirable to develop systems and methods to maintain multi-component contrast media in a mixed state throughout an injection proceeding.